In order to gather data on factors bearing on the etiology of colon cancer in man, studies have been initiated on the mode of action of chemicals causing cancer of the colon in animal model systems. We have begun to study the metabolic fate of 1,2-dimethylhydrazine (or dimethylhydrazine, SDMH) utilizing the carbon-14 labelled and appropriate analytical, biochemical and biological techniques. Furthermore, we have undertaken to establish whether the carcinogenicity of this agent is modified by agents acting as enzyme inducers of a variety of chemical types. Also, we are in the process of inducing colon cancer in an inbred strain of guinea pigs, strain 2, in the hope of establishing eventually a transplantable colon cancer in the species. In the metabolism studies we found that commercially labelled SDMH needed further purification by a chromatographic system we necessarily developed. The purified chemical injected into male Fischer strain rats was excreted in urine accounting for 4-7% of the isotope in the bile, of biliary fistular rats 0.7% and most of the dose was found in the expired air, approximately 50%. In intact animals the urine contained about 20% after 24-48 hours, the exhaled air 50% and about 1% in feces. The major portion of the radioactivity in the expired air is monomethylhydrazine and carbon dioxide accounts for much less radioactivity. Other metabolites are present. The urine contains both SDMA and monomethyl metabolites soon after injection. Later, unidentified components appear. After 24 hours, tissue levels of isotope decrease from liver to kidneys to colon.